1. Field of the Invention
This invention generally relates to the synthesis and recovery of energetic materials, especially for use in gun and rocket propellants and explosives. More specifically, the invention relates to the synthesis and recovery of nitramines.
2. Description of the Related Art
Nitramines are highly energetic compounds having found wide acceptance in the art of explosives and rocket propellant. The most common nitramines in use in the explosives and propellant arts today are 1,3,5-trinitro-1,3,5-triaza-cyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane (HMX). The acceptance of RDX and HMX in the art is generally attributed to the high energetic performance and the high energy density possessed by these compounds. In essence, RDX and HMX are the standards of energetic performance and energy density by which other energetic compounds are measured.
A drawback to RDX and HMX is that these nitramine compounds are relatively sensitive to shock, friction, and impact. The high sensitivities associated with RDX and HMX make these nitramine compounds less desirable for some applications, especially where the compounds are used or stored in an environment in which traumatic stresses may be encountered. By way of example, in a military conflict, the traumatic impact of hostile ammunition into a rocket motor or weaponry carrying RDX or HMX can lead to destruction of surrounding objects and loss of human life. In the event that the impacted rocket motor or weaponry is in proximity to arsenal or other explosive or combustible materials, catastrophic damage may result.
There is thus a need in the art to provide a highly energetic and high energy density compound that is relatively insensitive to physical stimuli, such as shock, impact, and friction. Various other nitramine compounds have been synthesized towards this end. For example, U.S. Pat. No. 4,085,123 to Flanagan et al. describes the synthesis of the nitramine compound 1,3-diazido-2-nitrazapropane (DANP) as an energetic liquid plasticizer for solid propellants. According to Flanagan et al., the DANP azide plasticizer is synthesized by generating a solution of 1,3-diacetoxy-2-nitrazapropane and dioxane and saturating the solution with anhydrous chloride gas. The use of anhydrous chloride gas makes this process extremely hazardous. In this regard, the Flanagan et al. patent states that the resulting DANP plasticizer is sensitive and must be handled with caution. Moreover, the acetate and chloride precursors are inherently impure, since their reactions reach and remain at equilibrium. In order to minimize the impurities, Flanagan et al. teach distilling both the 1,3-diacetoxy-2-nitrazapropane precursor and its chlorine analogue prior performing the reactions. On an industrial scale, these distillation techniques are impractical and highly hazardous.
Another nitramine synthesis route is disclosed in U.S. Pat. No. 5,243,075 to Cason-Smith, which describes contacting an N-acetoxymethyl nitramine with a mixture of concentrated hydrochloric acid and trifluoroacetic acid to produce the corresponding N-chloromethyl nitramine analogue. The chlorinated nitramines produced by this process are not sufficiently robust or chemically stable for effective use as an energetic material. The chlorine atoms of the N-chloromethyl nitramines are inherently unstable. When heated, hydrogen chloride gas is released. The presence of the HCl acid can lead to degradation of the material via autocatalysis.
The synthesis of 1,3-bis-(3xe2x80x25xe2x80x2-dinitro-1xe2x80x2,2xe2x80x2,4xe2x80x2-triazolo)-2-nitrazapentane (BNTN) is also known. BNTN has the following structure: 
Specifically, it is known to produce BNTN by suspending sodium dinitro-1,2,4-triazole in dry acetonitrile, and adding 2-nitraza-1,3-dichloropropane. It is believed by the inventors that the 2-nitraza-1,3-dichloropropane is prepared by reacting 2-nitraza-1,3-diacetoxypropane with an inorganic chlorinating agent, such as phosphorus pentachloride (PCl5). According to this method, however, the 2-nitraza-1,3-diacetoxypropane must be purified by distillation prior to chlorination to avoid the formation of chlorine by-products. Another distillation step is needed prior to the reaction of the 2-nitraza-1,3-dichloropropane with the sodium salt of dinitro-1,2,4-triazole. The hazardous nature and toxicity of 2-nitrazapropane and its by-products make distillation highly undesirable and impractical to produce on an industrial scale. Further, the 2-nitraza-1,3,-dichloropropane is very electrophilic and may react with incidental moisture to replace the chlorine atoms and form hydroxymethyl nitramines, thus complicating the nucleophilic addition of the triazole.
The inventors have found that the technique disclosed in the Cason-Smith patent is not suitable for making BNTN. The conditions set forth in the Cason-Smith patentxe2x80x94e.g., treating with HCl and trifluoroacetic acidxe2x80x94were insufficient to drive the reaction of 2-nitraza-1,3-diacetoxypropane and, as a consequence, a largely impure product was obtained.
This invention provides a synthesis route for preparing and recovering nitramine compounds having one or more N-heterocyclomethyl groups. The nitramine compounds preferably possess relatively high energetic performance, comparable or superior energy density, and relatively low sensitivity to physical stimuli (e.g., shock, friction, and impact) in relation to the current standards of RDX and HMX.
This invention also provides a method by which an N-heterocyclomethyl polynitrazaalkane can be precipitated at high yields from a solvent that forms a clathrate with the N-heterocyclomethyl polynitrazaalkane.
This invention further provides a method for synthesizing a triazole, such as 3,5-dinitro-1,2,4-triazole.
This invention still further provides a method for synthesizing a salt of a triazole, especially dinitrotriazole.
It is to be noted that, as used in the specification and the appended claims, the singular forms xe2x80x9ca,xe2x80x9d xe2x80x9can,xe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, by way of example, the term xe2x80x9cpolynitrazaalkanexe2x80x9d includes in its definition not only a single polynitrazaalkane, but also a combination of two or more polynitrazaalkanes.
The term xe2x80x9cpolynitrazaalkanexe2x80x9d means a nitrazaalkane having two or more nitraza (nitramine) groups. A nitraza group may be internally positioned along the azaalkane chain, or can be at a terminal position.
In accordance with an aspect of this invention, N-acetoxymethyl nitrazaalkane having an azaalkane chain (or backbone) of at least five atoms is halogenated to form an N-halomethyl nitrazaalkane. The N-halomethyl nitrazaalkane comprises at least one halomethyl moiety having a halogen atom, with the halogen atom comprising chlorine, bromine, or iodine. A salt of a heterocyclic nucleophile is reacted with the N-halomethyl nitrazaalkane to form an N-heterocyclomethyl nitrazaalkane. The solvent in which the nucleophilic substitution takes place forms a clathrate with the N-heterocyclomethyl nitrazaalkane. In accordance with the teachings of this invention, the N-heterocyclomethyl nitrazaalkane may be precipitated in a nonsolvent and recovered from the nonsolvent.
In accordance with another aspect of this invention, a method is provided for N-heterocyclomethylating a terminal nitraza moiety or terminal nitraza moieties of a polynitrazaalkane. In accordance with the teachings of this invention, the N-heterocyclomethyl polynitrazaalkane may be precipitated in a nonsolvent and recovered.
In accordance with still another aspect of this invention, a method is provided for preparing 3,5-dinitro-1,2,4-triazole or a salt thereof. The method comprises nitrating 3,5-diamino-1,2,4-triazole in an acidic solution having a pH not greater than about 3 to form 3,5-dinitro-1,2,4-triazole. The 3,5-dinitro-1,2,4-triazole is extracted from the acidic solution with little or no neutralization, so that the pH of the acidic solution during extraction is no greater than about 3. Optionally, the 3,5-dinitro-1,2,4-triazole may then be treated with a base to form a 3,5-dinitro-1,2,4-triazole salt.